I've spent a lot of time recently using iTunes, my last hobby was meticulously re-tagging my entire 20,000 song library. Over this time, I have come across a few niggling problems and possible improvements to the program so have decided to mock up an interface redesign.
The past few updates for iTunes have focused on new features like Ping & Books, and also tried to make iTunes a hub for music, movies & TV. My redesign tries to strip back some of the bulk and give a better music library browsing service.

The first part that needed redesigning was the top console, which looks out of place next to other OS X applications, with its frankly bizarre vertical 'signal buttons' and the outdated faux LCD central screen.

My design takes heavy influence from the current Quicktime player, dropping the fussy outlines around buttons, allowing a more streamlined and clearer arrangement.
For the list view, I decided to place more information next to the artwork of albums, leaving more space horizontally for variable data. The most obvious change from the regular iTunes is the revised genre tagging system, allowing for albums to be 'tagged' with multiple genres, thus enabling creation of more coherent playlists. The bottom toolbar has been completely removed, with the shuffle & repeat buttons relocated alongside other playback related buttons in the top section, and the remaining buttons sitting underneath the album artwork on the left hand side. The library information can be toggled on or off with the blue 'i' icon. Removing this bottom bar cleans the interface further, giving a less cluttered browsing experience.

In Coverflow, a button on the left toggles to hide/show the left menu, again giving more room for browsing. Also, the black top menu sits above the Coverflow much more comfortably than the old grey version.

A new playlist creation feature I decided to add takes inspiration from last.fm's Event Map. This view allows the user to choose one or multiple areas of the globe and hear a personalised playlist of bands originating from the selected cities. This is an easy way to create smart playlists that can quickly & easily capture a certain time in a certain part of the world. For example:

If you released the redesign would it automatically overwrite my existing iTunes (like an update does) because I'd like to use it too but couldn't stand the hassle of dealing with moving all the music over.

@!Greenehouse: IF he would make it into a real mod you would only have to replace some minor files merely for the UI itself. Nothing big that forces you to move your music or anything else. On the downsite you would have to replace these files every time iTunes gets an update.

Given that you've manually tagged a 20,000 song library I'm shocked that you didn't add things like being able to bulk change the sort order fields. It drives me crazy that I have to manually change the sort by artist and sort by album artist fields on a tedious and slow song by song basis.

One big glaring hole in iTunes is the fact that you've got one set of columns and one sort order for the entire library. If you have a mix of music that is typically sorted by Artist (most 20th and 21st century music) and music that is typically sorted by composer (pretty much everything older) there is no one sort order that is going to work. Changing the artist to match the composer is unacceptable because there's a huge difference between Glenn Gould playing Chopin and Sergei Rachmaninoff playing Chopin.